A MÖSSBAUER SPECTROSCOPY STUDY OF A STRUCTURAL PHASE TRANSITION IN TNE PEROVSKITE TYPE LAYER STRUCTURE COMPOUND (CH3NH3)2FeCl4, A 2-D ANTIFERROMAGNET

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A MÖSSBAUER SPECTROSCOPY STUDY OF A STRUCTURAL PHASE TRANSITION IN TNE

PEROVSKITE TYPE LAYER STRUCTURE COMPOUND (CH3NH3)2FeCl4, A 2-D

ANTIFERROMAGNET

C. Nicolini, W. Reiff

To cite this version:

C. Nicolini, W. Reiff. A MÖSSBAUER SPECTROSCOPY STUDY OF A STRUCTURAL PHASE TRANSITION IN TNE PEROVSKITE TYPE LAYER STRUCTURE COMPOUND (CH3NH3)2FeCl4, A 2-D ANTIFERROMAGNET. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-295-C1-296. �10.1051/jphyscol:19801105�. �jpa-00219586�

JOURNAL DE PHYSIQUE Colloque C l

,

supplkment au n O 1, Tome 41, janvier 1980, page C1-295

A K~SSBAUER SPECTROSCOPY STUDY OF A STRUCTURAL PHASE TRANSITION I N TNE PEROVSKITE TYPE LAYER STRUCTURE COMPOUND ( C H ~ N H ~ ) 2 ~ e ~ 1 4 , A 2-D ANTI FERROMAGNET

C. N i c o l i n i and W.M. R e i f f

Chemistry Dept. Northeastern University, Boston, Mass. 02115, USA.

(CH3NH3)2FeC14 belongs to a group. of compounds, ( C , H ~ ~ + ~ N H ~ ) ~ M C ~ ~ (M=Mn ,Fe,Cu,Cd)

,

which crystal - lize in a perovskite-like structure consisting of layers of corner-sharing MC16 octahedra. The layers are widely separated by (CnH2n+1NH3) groups.

In addition to the interesting 2-D magnetic prop- erties, these compounds exhibit a number of struc- tural phase transitions governed by the reorien- tation and ordering of the alkyl ammonium ions (which are influenced by N-H. ..Cl hydrogen bonds) and changes of the tilt systems of the octahedra layers. For the particular compound

(CH3NH3l2FeCI4, Knorr et a1

.

^, found two struc- tural phase transitions: 1 ) a continuous order- disorder transition from a high-temperature tetra- gonal to an orthorhombic phase at 328K and 2) a discontinuous transition to a low-temperature tetragonal modification at 231K, using optical birefringence, x-ray and neutron diffraction tech- niques. Keller et a ~ . ( ~ ) have studied the Miss- bauer spectra of a powder sample of (CH3NH3)2FeC14 as a function of temperature in the range 100-300K and reported no indication of the phase transition at 231K. In this work we present results of a 57~e Mtissbauer study of a polycrystalline sample of

(CH3N~3)2Fe~1 for which there was no pulverization or dilution. We have found clear evidence of the structural phase transition at 231K reported by Knorr et a1 .(2) The transition starts at % 265K and it does not go to completion for temperatures as low as lOOK even after long periods (2-3 days)

of thermal equilibration. The Mtisibauer spectrum at 294K of this material consists of a quadrupole doublet with an isomer shift (relative to Fe metal) of 1.096 mm i1 and ~ ~ t ) = 2 . 2 6 1 mi1. These values agree well with those reported in the literature

(4). The Mtssbauer parameters for the new coexist- ing phase are 6(B)=l .I98 mi' and

ALP=

^{1.343 mm: 1}

( F i g l ) 1 , ^I , I ^{I I I}

1 1

Velocity (mm/sec) Relative to Iron Fig. 1 Missbauer spectrum of (CH3NH3)2FeC14 at

231 K.

From the Lorentzian fit of the spectrum shown in Fig. 1, the intensity ration .IA/IB can be calcu- lated and is .L 1.18. The A€ value indicates

Q

higher symmetry for the local coordination invirow ment of Fe in the latter3phase, The same poly- crystalline and undiluted sample was finely ground and a redetermination of the Mtssbauer spectrum as a function of T showed no evidence of the phase transition. Apparently sampl e grinding 'introduces defects such that no transition occurs. We believe

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801105

c1-296 JOURNAL DE PHYSIQUE

that this is one of the reasons that the phase transition was not observed in the previous study!3) Work supported by NSF-DMR-77-12625

/1/ W. Depmeier, J. Feische and G. Wildermuth, J. Solid State Chem.,

1,

(1977), 57.

/2/ K. Knorr, I.R. Jahn and G. Heger, Solid State Comm.,

15,

(1 974), 231.

/3/ H. Keller, W. Kiindig and H. Arend, J. de Physique, Col loque C6, 37, (1976), C6-639.

/4/ M.F. Mostafa and R.D. Millet, Physical Review,

B, 4,

(1971), 2213.